relax SVN archive

Documentation fix for the assemble_coord_array() function.

The return values for lib.structure.internal.coordinates.assemble_coord_array() were incorrectly
documented.

Converted the structure.superimpose user function to the new pipes/models/molecules/atom_id design.

The user function arguments have not changed, however the backend now uses the new
pipe_control.structure.main.assemble_coordinates() function. This is to simply decrease the number
of failure points possible in the structure user functions. The change has no effect on the user
function use or results.

Created the internal structural object model_list() method.

This is to simplify the assembly of a list of all current models in the structural object.

Converted the structure.rmsd user function to the new pipes/models/molecules/atom_id design.

This allows the RMSD calculation to work on atomic coordinates from different data pipes, different
structural models, and different molecules. The user function backend uses the new
pipe_control.structure.main.assemble_coordinates() function.

The Structure.test_rmsd_molecules system test has been updated for the user function argument
changes.

Docstring spelling fixes for the steady-state NOE and relaxation curve-fitting auto-analyses.

Updated the Structure.test_displacement_molecules system test.

This is for the changes to the structure.displacement user function.

Another refinement for the structure ID strings returned by the assemble_coord_array() function.

Converted the structure.displacement user function to the new pipes/models/molecules/atom_id design.

This allows the displacements to be calculated between atomic coordinates from different data pipes,
different structural models, and different molecules. The user function backend has been hugely
simplified as it now uses the new pipe_control.structure.main.assemble_coordinates() function.

The Structure.test_displacement system test has been updated for the user function argument changes.

Converted the internal structural displacement object to use unique IDs rather than model numbers.

This allows the object to be much more flexible in what types of structures it can handle. This is
in preparation for a change in the structure.displacement user function.

More improvements for the structure ID strings returned by the assemble_coord_array() function.